The invention relates to an electric lamp having tubular cap mainly consisting of metal, and a lamp envelope having a pinch. An electric light source is arranged in the envelope, and source current conductors extend through the pinch to the exterior and are electrically connected to the cap, the pinch being received with a clamping fit by a metal sleeve secured in the cap.
An electric lamp of this kind described in the non-prepublished European Patent Application No. 82200902, to which U.S. Pat. No. 4,495,436 has the advantage with respect to conventional lamps that the cap is secured to the lamp envelope without cement, whilst nevertheless the lamp has a pretermined focal length (=distance of the light source from a reference point on the cap). It is important to avoid the use of cement because heat and time are required for hardening and cement in warm surroundings is decomposed and can crumble off.
When lamps are used in an optical system, it is of importance that the light source occupies a predetermined position. Accurate positioning requires that the light source be arranged in a predetermined position with respect to the cap. In the lamp according to the aforementioned U.S. Pat. No. 4,495,436, the focal length is adjusted, it is true, in a direction parallel to the cap axis but a lateral displacement of the light source with respect to the cap axis is not possible. The lamp cannot be aligned in three dimensions and therefore cannot be utilized for all applications.
A lamp is known from Dutch Patent Specification No. 64742, in which a sleeve is secured to the lamp envelope by means of a cement. A cap is provided on the sleeve, the cap having at its open end an inwardly bent edge, which surrounds the sleeve with clamping fit. Two diametrically oppositely arranged tongues are pressed out of the sheath of the cap to the interior and are welded to the sleeve. Although in this lamp the focal length is adjustable, a three-dimensional alignment is not possible.
A method of securing without cement a lamp envelope provided with a pinch in a cap with the aid of a tubular inner part which receives the pinch with clamping fit is known from German Offenlegungsschrift No. 2938189, to which U.S. Pat. No. 4,371,807 corresponds. The inner part, provided with inwardly bent pairs of lugs for receiving the pinch of the envelope, closely engages the cap so that also in this case a longitudinal movement and a rotary movement of the lamp envelope with the inner part opposite the cap is possible, but a pivotal movement about transverse axes is precluded.
From the British Pat. No. 450,948 an electric lamp is known, whose lamp envelope is secured with the aid of cement in a spherically curved ring, which could be aligned in three dimensions with respect to the cap. The connection between the cap and the inner part is made by means of soldering, for which purpose the cap is provided with three holes for receiving the solder. These holes containing the connection solder limit the alignment process, more particularly in the longitudinal direction.
A manner of holding the pinch of the envelope is known from German Pat. No. 140,817, to which British patent application No. 2,042,823A published Sept. 24, 1980 corresponds.